text:
Forward Slip - Which speed to maintain?
Which is the proper speed to be maintained during a Forward Slip? Near Vfe or Vref? Which one will let you lower with the shorter ground distance and why?

What type of aircraft are you flying?

General Aviation, a Cessna 150 for example.

Don't ever slip at the landing speed.  That speed is calculated to be 30% above the stall.  When you slip the stall speed increase could be greater than 30%.

Keep in mind that in many aircraft the ASI is completely unreliable in a slip, typically reads way low.

The purpose of a slip is to make drag, and the faster you go, the more drag you make.  In a slip your aircraft is no longer in a "slippery" low-drag condition.   So full rudder, and put the nose way down--the need to disappate the excess airspeed before flaring can be accomodated by picking a round-out point further away from the threshold.

@quietflyer "The purpose of a slip is to make drag, and the faster you go, the more drag you make." Technically true of course, but if you are slipping it is because you have excess energy to dissipate. Pumping up the drag number by adding more kinetic energy isn't the goal here...

More food for thought from C-172S POH:  "Steep slips with flap settings greater than 20° can cause a slight tendency for the elevator to oscillate under certain combinations of airspeed, sideslip angle, and center of gravity loadings."

Vfe is quite fast to be flying on a landing approach slipping or not, although I suppose there's nothing stopping you from doing that if you need to dive that steeply. You still end up with excess energy and will land long. What matters in the end is your energy state as you get to a few feet above the ground crossing the threshold.
A moderate speed safety margin above landing flap approach speed is sufficient. Keep in mind that a calibration error is created when the pitot is angled off the airflow and the airspeed will read a little lower than when straight.
If I'm approaching at 70kt and start slipping to lose altitude, I push over a bit to bring the airspeed up to 75 or 80 kt during the slip to have some safety margin against stall/spin. As I get close to the surface, I'll ease the nose up while keeping the slip in to bleed off the excess speed, then straighten out, more or less in one motion.
If I really messed things up and find myself too fast/long as the flare is coming up, I'll keep the slip in place right into the flare, straightening just before touchdown.
In the end, you slip at the lowest speed that is safe, only going faster because you need to dive more steeply, and are aware that you will arrive at the threshold with excess energy that still has to be dissipated.

Indicated Airspeed in a slip is unreliable, so forget trying to fly an airspeed. The simple and reliable way to control speed in a slip is to fly to correct pitch. What is the correct pitch? How about the same pitch you were using for the stabilized power off approach prior to the slip, (pitch for 1.3 Vso)? Then when you exit the slip your indicated airspeed will return to what it was before you entered the slip. Simple. If you are concerned about stalling lower the pitch slightly, but realize that you will be faster than 1.3 Vso when you exit the slip.  I've used this method for 50 years and have never stalled... ;).

In my concern, a forward slip should only be used during an emergency. If you are unstable, you should go around. In case of an emergency, what would you do?

For a wings level, power-off descent first principles say that the flight path angle (assumed > -10 deg) is approximately the arcsin of drag over lift, D/L.  For full-pedal trims, that small angle assumption may not apply. Furthermore, the equations of motion are more complicated. All 6 degrees-of-freedom have to be considered. For example, the resulting bank angle and side force will uniquely vary as a function of speed. FAA-H-8083-3C (p. 9-13) says the steeper your bank angle in the trim, the higher the descent rate (not necessarily angle). I would interpret that as not only higher drag but the lift vector getting more away from vertical. “…the point may be reached where full rudder is required to maintain heading even though the ailerons are capable of further steepening the bank angle…increase in airspeed increases rudder effectiveness permitting a steeper slip.” [emphasis added]
So, there’s a tradeoff unique to every configuration both in terms of the balance of roll and yaw control power available vs. speed and in terms of resulting rates of descent vs. forward motion. Sounds like the flight test method is a way to go (if you can get a good source of angle of descent data and account for winds on each run).

First and foremost is safety.  There is no general answer because each aircraft model has its own safety margin when flying cross controlled.

Seek expert advice, and always try the slip at altitude first.

Consistent speed is important for judging approaches because aircraft kinetic energy is proportional to the square of velocity.  Excessive speed can really butcher an approach.
With the Cessna 172 I was lucky to find that forward slips could be done at my favorite approach speed: 65 knots.  That is exactly 1.3 of the flaps up stall speed of around 50 knots.
This enabled a forward slip with out any great change in approach speed.  Just used it when a little high. Rounding with excess speed can have one floating down the runway for an uncomfortably long time.

For a constant rate of descent, the slower of the two airspeeds will shorten the ground distance.  This is because you are covering less horizontal distance for the same altitude lost.

IMO, this answer isn't really helpful. It's factually correct, true. However the core tenant, that there is a constant rate of descent, is misleading as that would not be the case with a faster dive in a slip.

@KennSebesta, sometimes my brevity is intended to highlight a question that is not well thought out.  If the OP cares enough to bite, both the question and my answer evolve through our engagement.  This one just withered on the vine…

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What are the meanings of various reference lines and sections in a take-off distance graph?
I am trying to solve a numerical problem related to determining take-off roll using a take-off distance graph. The parameters are Temp: 90F, Press. alt: 2000ft, wt: 2500lbs, headwind: 20 Knots. I got the following graph (solid red lines):

My questions/clarifications are as follows:

It looks like the first reference line is the "density altitude", correct?
Looks like the second section of the graph is a relationship between aircraft weight and take-off roll (where take-off roll distances are represented vertically on the second reference) at various density altitudes. This seems to make sense because for a certain weight, if I go up, meaning I intercept higher density altitudes, the take-off roll increases.
It is not very clear to me the plotting of the diagonal lines. The way I understood it is that they go from the point of interception of the reference line to a point on the vertical weight line which is midway between the inclined curves intercepting that vertical weight line.

You need to read such graphs strictly from left to right. Each new panel adds the influence of another parameter, and when you are done, the result is corrected for altitude, take-off weight, wind and obstacle height. Except for the leftmost panel, the groups of lines only help you to find the correct slope and do not represent a certain altitude.
You start with the outside air temperature. Pick what the instrument in your cockpit indicates, and go from the temperature axis straight up until you intercept the line which is closest to your given pressure altitude. This can be read directly from the altimeter if it is set correctly. You can try to interpolate between lines, but to be safe pick the next higher value.
Next, move horizontally to the first reference line. From there, follow the slope of the lines until you intercept the x-position which corresponds to your aircraft's mass. If you start between two lines, you should move such that the relative vertical distance to the neighboring lines does not change. Note that the take-off mass is also a value you should know already if your preflight was done properly.
From that point, jump off horizontally until you intercept the next reference line. Depending on wind direction, follow either the dashed or the solid lines until you arrive at the x-position which corresponds to the wind component in runway direction. You will note that for headwind you will move slightly down, so headwind shortens the take-off distance. Makes sense, right?
The last panel helps you to find both the take-off roll (obstacle height zero) and the take-off distance over a 50 ft obstacle. Here you can only extract the values at the x-positions 0 and 50 and interpolation will not work. The y-axis all the way on the right now will tell you the distances in feet.
The reference lines show the values for the standard take-off at MTOW and calm wind. The examples given by the red lines are for two different situations:

Solid red line: OAT is 90°F, pressure altitude is 2000ft MSL, take-off mass is 2500lbs and with a headwind of 20kts the take-off roll is 500ft. At this point your speed should be 62kts (see table).  This is the result for your first question.
Dashed red line: OAT is 15°C, pressure altitude is 6000ft MSL (rounded up from 5650ft), take-off mass is 2950lbs and with a headwind of 9kts your take-off roll is 1400ft and the distance needed to clear the 50ft obstacle at 1.3*stall speed is 2300ft.

Why to the Fahrenheit and Celsius scales on the left-hand graph not line up properly? It seems to show 0°C = 50°F.

Peter, Thanks for your reply. Very good info. Some follow up questions. I still am finding it hard to understand how to plot the diagonal or inclined plots (the part you discuss in your third pararaph). You say "follow the slope of the lines", does this mean stay parallel to either or both lines? This is not very clear to me.

It means you should maintain at the same position relative to the two lines. If you start in the middle, you should stay halfway between the two lines. Basically, it's a visual way of interpolating between the two lines.

The diagram is a sample from the FAA Airman Knowledge Testing Supplment (page 40).  The Fahrenheit/Celsius scale error was a known issue and has been corrected in current versions, including the one I linked to.

And for the original poster, I should add that the graph is also used in chapter 10 of the Pilot's Handbook of Aeronautical Knowledge, including a detailed description of why and how to use the chart and sample problems.

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sort: votes


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Do jets use tinted windows?
For cars, I've heard of LLumar used as window tint.
Do jet aircraft use window tint? If so, what type of window tint do they use?

Like any specifics I don't know what this means.  Is there an alternative phrase that you could use?

I guess the OP wants to know if jets use window tint, (no they don't) and if they do, which brand of tint specifically.

Yes, airplanes (all types including jets) can use window tints.
Ultraviolet "A"
Tints for airplanes are with enhanced protection from UVA radiation. UVA exposure can increase the risk of skin cancer and will damage most organic materials. Its intensity increases about 5% with every 1000 feet of altitude. Unlike car tints, airplane tints need to block the additional exposure to UVA.
Solar Energy Control
Tints also block near-infrared radiation which results in lesser interior heat.
LP Aero Plastics (product listing) and PolyOne are the two manufactures I found for aircraft tints.

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How can I identify a low flying plane at night over Bangalore?
I often see a low flying plane circling over south Bangalore around 00:30-01:00. It circles at least twice and it's not very big, mostly the size of a private jet.
How can I go about identifying it?

Snap a photo and post it here!
Or maybe go look at flightaware.com the next time you see it!

A night photo?!

On Nov 12 at about 1845 UTC, which would be about 1215 local on Nov. 13, a Vistara A320, reg. VT-TTM, took off from BLR and did several touch-and-go’s at VOBG then returned to BLR.
On Nov. 10, around the same time, another Vistara A320, reg. VT-HYD, did the same thing. Taking off from BLR, doing touch-and-go’s at VOBG before returning to BLR.
According to this article @pondlife found, VOBG airport is open for pilot training.

@mins It’s clearly touch-and-go’s at VOBG runway 27. Why T&G’s in an A320 in the middle of the night? I have no clue.

@mins I think pondlife figured it out. See edits

I was hoping this to be something slightly more exciting like some secret electronic surveillance research program etc :D ... many thanks for your response.

Lol! Sorry to burst your bubble :P

so I did track it on flightaware this time (0119 AM IST) it took a couple of minutes (~10) to circle twice. It should be IAD9109, but I couldn't get more details probably its Indian airlines(Air India) this time, my google fu didn't work.

@amritanshu You said in your question it looked like a small jet. Likely there are private aircraft taking advantage of the training opportunity too. Depending on their xponder type they might not track on FR24.

https://uk.flightaware.com/live/flight/IAD9109 this was it! the details were not available last night.

An ADS-B receiver is the best way to identify an aircraft flying overhead, in most cases. This can be built from about $50 USD, but may be more.
Put simply, you would need

A USB SDR receiver
An Antenna
A computer to connect the reciever to, and run software on
Decoding software (at a minimum, dump1090

Instructions on specifics can be found here: https://www.adsbexchange.com/how-to-feed/adsbx-custom-pi-image/
The Raspberry Pi can be replaced by any Linux computer, really.

This is the meta answer :)... Pretty cool. Many thanks!

SO is about giving the guy a fish and teaching him how to fish. :o)

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Is it always required to calculate the fuel for an IFR alternate?
I was asked to plan a cross country flight from KTMB (Miami Executive Airport) to KTPA (Tampa International Airport). After doing all the planning, I realized I needed to calculate the fuel for an alternate airport.
According to 14 CFR 91.167, fuel is required from departing airport to intended destination airport, plus from intended destination airport to alternate airport, and another 45 minutes of flying at normal cruising speed.
In 1-2-3, if weather forecasts tell that 1 hour before and 1 hour after the ETA, the ceilings would be less than 2,000 feet and less than 3 statute miles visibility, I need to file an alternate airport.
But if the forecasts tell that at KTPA, the weather conditions will be better than that, would I still be required to calculate the fuel for an alternate?
If the conditions are worse than that, then how would I calculate the fuel to my alternate, which I chose to be KSRQ (Sarasota–Bradenton International Airport). Do I need to do again the SID at KTPA, then enroute and then STAR and approach at KSRQ, or just a direct flight?

The only rational approach is to consider the worst alternate conditions at the expected TOA and plan direct only if good VFR is the condition otherwise plan it IFR.

You only need an alternate if a) the weather is below the minimums you mentioned, or b) your destination has no instrument approach. That's in both 91.167 (IFR fuel requirements) and 91.169 (IFR flight plan requirements), e.g.:

§91.167   Fuel requirements for flight in IFR conditions.
(a) No person may operate a civil aircraft in IFR conditions unless it
  carries enough fuel (considering weather reports and forecasts and
  weather conditions) to—
[...]
(2) Except as provided in paragraph (b) of this section, fly from that
  airport to the alternate airport; and
[...]
(b) Paragraph (a)(2) of this section does not apply if:
[...]
(2) Appropriate weather reports or weather forecasts, or a combination
  of them, indicate the following:
(i) For aircraft other than helicopters. For at least 1 hour before
  and for 1 hour after the estimated time of arrival, the ceiling will
  be at least 2,000 feet above the airport elevation and the visibility
  will be at least 3 statute miles.

As for how to calculate the fuel requirement to your alternate, I would just plan a direct route (or whatever you need to avoid restricted airspace etc.) and calculate your regular cruise fuel requirement. I don't see any point in trying to anticipate in detail what would happen if you actually have to divert because you just can't know that anyway.
IFR Magazine has a nice article on planning alternates that might help you with some of the practical details.


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What is the typical voltage and frequency of the electrical generator in an airliner?
How many volts does the typical airliner CSD (Constant Speed Drive) produce?  I've read the CSD's output is typically 3-phase 115 VAC @ 400 Hz. Is that correct?
I've also read the typical airliner generator puts out "in-phase 28 VAC". Is that correct?
Does the CSD provide more voltage than the generator needs and the generator reduces the voltage via a transformer?

You keep referring to power but I think you mean voltage. A transformer changes voltage, and "115-VAC @ 400 Hz" gives no power indication. For electrical circuits power would be expressed in watts.

Sorry, yes, I mean voltage.  I'll try to edit my question.

The CSD is not an electrical generator, its function is to rotate a shaft at a constant speed. The generator is then driven by this constant speed shaft. The CSD and the generator can be under the same casing, it's named an Integrated Drive Generator (IDG).

Yes, I understand the CSD itself is not a generator.

anyone got a problem with 'typical airliner'?  what happened to aviation SE?

A constant speed drive (CSD) converts the rotation from the accessory gearbox to a predetermined constant rotation rate.  The rate of the accessory gearbox is directly related to the high pressure spool (N2) rate and changes with power adjustments.
The CSD will ensure its rotation rate is constant.  The Challenger 604 CSD rotates at 12,000 RPM and outputs 115 VAC @ 400 hertz.  Its max output is something like 30 kVA or kilovolts-amps.  Since we are talking AC power, it is not appropriate to call that watts.  The AC power is converted to 28 VDC by the way of transformers called transformer rectifier units (TRU).

So in my comment above about CSDs producing "3-phase 115 VAC @ 400 Hz" and airline generators producing "in-phase 28 volts AC", is there a transformer in between the CSD and the generator???

No.  Most airlines have AC generators or a better term AC alternators.  That power goes to power the AC buses and the TRUs. The power outut from the TRUs power the DC buses.  The transformer is between the AC alternators and DC buses.  There are no DC generators.  At least on my airplane.

Smaller jets such as the Hondajet HA-420 and Embraer Phenom 100 & 300 use 28 VDC starter/generators (325 Amp to 400 Amp).
Larger jets may use a variety of 3 phase 115 VAC @ 400 Hz generators, 28 VDC generators, or in the case of the Boeing 787, a variable frequency starter generator -

787 Engine start system schematic—GEnx
  The variable frequency starter generator is a six-pole machine within an aluminum housing driven directly from the main engine gearbox. The generator     is a brushless, three-phase, alternating current, and variable frequency synchronous machine. It has a nominal rating of 235 volts alternating current (VAC), 250 kVA, three phases, and 360–800 Hz output.

787 Propulsion System


text:
Pilot passed out in a small GA plane. What can a passenger do?
There is another question about airliners and if someone not qualified could land them. My question is about the steps I should take to stay alive in a small GA plane.

Let say a friend of mine invites me aboard a small aircraft (like Cessna 172 or equivalent).
At some point my pilot friend passes out for some reason. What should I do considering the following:

I'm not a pilot.
I'm seated in the co-pilot seat.
I spent hundreds of hours on Flight Simulator (a few years ago).
I've been initiated to fly a small aircraft (1 session covering the very basics), but no take-off/landing exercises.
The weather is good.
Aircraft is in good condition.
The tank is full.
Area has ATC and I know how to operate the radio.

This is my guess:

Hold the plane's level and heading
Slap my friend to try to wake him up
Send "Mayday" asking for assistance and technical guidance
Try to follow ATC instructions as well as I can

Does this look good? What should be done differently?

possible duplicate of Can a passenger realistically replace suddenly incapacitated pilots?

@Simon I already saw that question, but mine is not "can I?", it's about "How do I?" ;)

The answers, comments and off-site links do provide everything you've asked for.  The main thing is to throw away the Flight Simulator experience.  The handling of a real aircraft is nothing like the PC simulations.

Yeah, if you talk about feeling the plane. But I least, I know how control surfaces work, what I'm supposed to expect if I touch this button and what a transponder looks like :)

Very true, and on reflection and your edit, I've retracted my VTC.

By the title of the question, I was going to say "First: Get out of stack exchange!"

@Malavos On my checklist it was: 1. Take a selfie 2.Post it on Facebook 3.Go to SE 4.Aviate :')

@Simon: There is a confusion between default FSX and some very good add-ons like PMDG 737 NGX. It's not sufficient to actually land a B737 but it's not so bad either:  I have [...] 12 [years] on the 737 NG [...] PMDG's NGX in my experience is extraordinarily good [...] I use it to prepare for sims and Cat C airfields and it is invaluable. The system interaction and fidelity is excellent and with far less glitches and sim-isms than many commercial sims [...] (PPRuNe).

@mins.  I know, I've got about a thousand hours on it.  Fine for systems and autopilot, lousy for hand flying and not relevant at all for GA ;)

First, check that you yourself are OK, and not experiencing symptoms of hypoxia due to altitude or an exhaust leak. That's a whole different kind of emergency.

The question says small plane, not an airliner. Such is probably much easier to crash-land surviving.

I like the comment take selfie post on face book etc etc. aviate, it made me laugh... Wish I'd thought of it... However you must keep the aircraft level and get it under control immediately, if you don't feel like you are in control, you will panic very quickly and things will then go from bad to worse real fast. Everything else is secondary. Even facebook :-)

Best case scenario: You're straight and level, on frequency with some form of human being, there's no immediate danger and you have the know-how to transmit. In that case, that human will provide you with everything they possibly can to help you. Most important thing for you to do is keep the aircraft away from clouds, away from terrain and not panic. You'll probably be in an aircraft that is more-or-less easy to fly in this situation. Most GA aircraft are quite stable and will not be a beast to control.
Once talking to ATC they will tell you to set your transponder to a number. You should find somewhere a 4-digit readout with a knob below/above each digit. Set the number indicated to help ATC identify you easily.
Otherwise, look around you for big landmarks (Mountains, Lakes, even a large Church/Cathedral) as one of the first things ATC will want to do is work out where you are.

That's best case; let's look at some alternatives.
You're out of range of the tuned frequency on the radio, or there is no response:
Tune 121.5MHz, this is the emergency frequency. Someone will be monitoring this channel and be able to give you further advice - if nothing else a local ATC channel to tune. Failing this see if your pilot has a chart handy, he may have drawn his intended route on it - look along that route for anything that looks like a frequency to tune into the radio.
Aircraft is climbing, or descending:
Get the aircraft into safe, level flight. Remember controls work in the opposite sense to what you might expect (probably not if you've ever played any flight simulator). If the engine is roaring reduce power slightly. If you appear to be losing altitude with the nose on the horizon increase power slightly. Do everything with tiny incremental changes. Try not to fiddle too much with controls, only what is necessary.
Aircraft is heading directly for a cloud/out to the sea/towards a heavily built up area/a big airport:
Turn 180 degrees - don't try to turn too quickly, it should take roughly 30 seconds to 1 minute to complete this turn.

There are courses which are aimed at non-pilots who regularly fly in the right hand seat. Here's some interesting reading:
http://www.avweb.com/news/safety/183023-1.html

All answers were very good. I accept this one since it's the closest to what the question was about: what should I do. Thank you all guys! And wow 4000 views in less than 24 hours !

controls work in the opposite sense.  What do you mean by this?

@Simon pushing forward makes the aircraft go down, pulling back makes it go up. Unless you're flying upside down ;)

@WayneWerner But that's the "normal sense".  I still don't get the point about opposite sense.

@Simon - to anyone who has ever flown a flight sim (or even a space game!) it's normal sense. But for people who have never experienced either, pushing forwards [on a joystick/yoke] is akin to "up" and pulling towards is "down". It's perhaps a bit of a moot point, I think most people would work it out pretty darn quickly.

This has happened before and it usually ends ok, the most important thing is to keep calm. One suggestion I would have is instead of flying straight and level I would fly a box over the current location while you speak to ATC. This will keep you in range of the ATC station you are talking to and keep you out of trouble. If you fly straight and level the terrain may come up to meet you, you could fly out to sea, or you could blunder into O'Hare's airspace with all the fun that would ensue. Try to maintain the same altitude as if you are at cruise the mixture should be set for that altitude.
A few things to add to your list:

You need to apply carburetor heat about every 15 minutes unless the aircraft is fuel injected. If you don't do this your carb could ice up and you could lose power. This is done by pulling the carb heat knob (or lever, depending on the AC) for 20 seconds or so and then pushing it back in
Fuel management: depending on the aircraft you may need to switch tanks. A C172 (and most high-wing airplanes) is generally set to both tanks in which case it's not an issue but in low-wing airplanes you will need to regularly switch tanks (say every half an hour) to keep the fuel balanced, otherwise you could run out of fuel in a tank and down you go with a full tank in the other wing. On a PA-28 the fuel selector is by the pilot's left knee which would make things interesting. Make sure you don't accidentally switch the fuel off!
Slapping someone isn't the best way to wake them up, pinch their earlobe as hard as you can with as much fingernail as possible, or push a pen into it. It's very painful, if anything will wake him/her that's it

Thanks for your answer, very informative. If I tell ATC that I know nothing about the plane, should they be able to help me (by telling me step by step instructions, like you just did) or to find someone that could ?

They will find someone rated on the aircraft to assist.  This has happened in quite a few cases.

And should I throw a mayday in this situation? I'm pretty sure the answer is yes, but just to be sure...

Yes you should definitely declare an emergency. You are in trouble and need immediate assistance.

Even if you just manage to blurt out "mayday" and roughly where you are, that will be a major boost to helping you. Since you know what the transponder looks like, setting 7700 is also a major plus but this is part of the "communicate" bit.  There is no doubt that the scenario you describe is a critical emergency and you are entitled to make as much fuss as you can.

And there is a medical emergency with one of the occupants of the plane. Suddenly passing out can mean a heart attack.

On the mayday point, Im struggling to think of a more emergency situation than "Aircraft has no lucid qualified pilot at the controls"

The wings falling off would top that one in my book @Jamiec

@GdD - just. Although in that scenario I suspect ATC's response would be "Thanks for letting us know. May god have mercy.... Fire appliances enroute" (That is unless you're a crack israeli pilot who can fly with 1 wing)

@Jamiec Every time I see that video I wonder how they hell the special effects were done.  Still find it hard to believe, even though I know it to be true!

'Carb heat' as the first point? Makes no sense if there is no engine trouble.   And every 15 minutes? That's not in any POH of any plane I've ever flown.

I also think asking a non-pilot to fly a box (or even a circle) is pushing it. Too much to concentrate on, just keeping level in a simple turn is hard enough. Get it wrong (apply too much up elevator) and you'll stall - good luck knowing what to do then without training.

@Jamiec I tend to agree. If you're about to fly into O'Hare's airspace, whoever is on the other end of the radio will presumably let you know about that very quickly (and give you instructions to avoid doing so while coordinating with O'Hare to let them know what's going on.)

I second @rbp; the carb heat advice here is flat out wrong. It also might be unwise, depending on the situation, since the non-pilot wouldn't know what to look for if icing occurred and would blithely turn carb heat back off after 20 seconds...

@Simon - is there a video of the israeli jet in flight or on the ground that you can link to? Ive never seen it!

@Jamiec the skeptics question has a video; not sure if any of the in flight portions were taken from another aircraft or were all reconstructions.  Google has a number of pictures taken after it was on the ground:  https://www.youtube.com/watch?v=slLKmtIKccs  https://www.google.com/search?q=f15+1+wing&tbm=isch

@DanNeely - oh duh! You mean the question I answered. Of course ive seen the video. (I worry myself sometimes)

Carb heat and fuel management are far too much detail for someone who is not a pilot.

I don't know about that, telling someone to pull the little knob out that says "carb heat" doesn't seem like that big a deal to me.

Just thought I'd add an answer about "aviate", "navigate", "communicate" which is discussed somewhat in the comments and is a big part of what you should do.
It's simply a matter of dealing with the most important things in order.
Aviate - fly the aircraft (keep it flying) - if you fail to do this, it will almost certainly kill you.
Navigate - fly where you want to go.  In this case, do as little as you have to to avoid obstacles, terrain and clouds.  Don't worry about bimbling into controlled airspace - someone else will take care of it.  Don't try to be clever and fly circuits or boxes or whatever.  Without at least a few hours proper training, trying to navigate could well lead to you forgetting or failing to aviate.  Not navigating away from clouds, obstacles etc is the second most likely thing to kill you.
Communicate - tell someone about it.   Not doing this won't kill you but could stop you getting help with one and two not killing you.
Mayday on the frequency already tuned.  Use the mnemonic "Rest In Peace Louis Hoy" if you can remember it.  R for reason, I for intent.  P for position, L for level (altitude), H for heading.  If you can't handle it, a simple "mayday" will start the ball rolling.  If all you say is the word "mayday" or "emergency", if anyone hears you, they will reply "station calling, say again" or "station calling, pass your message" or similar.  This just means they got it, but don't know who you are.  The conversation has started, let the person you're talking to do the work and ask questions as needed.
If no-one replies, and you can remember the frequency, tune 121.5 - the international distress frequency for VHF.  Someone will hear that and quite likely be able to triangulate your position.  Tuning the transponder to 7700 will also get a lot of attention.
Do not communicate, even if someone is calling you, if it takes your attention away from aviating and navigating.  If you can, a simple "standby" in response will tell the caller all they need to know.
Sadly far too many people have died because they failed to follow this simple advice which has been proven over many, many years and 10s of thousands of urgent situations.
Remember.  In the ongoing battle between the Earth and aircraft arriving in other than controlled conditions, the Earth has yet to lose.

the Earth has yet to lose - Love it :)

"the Earth has yet to lose"  I'm going to +1 just for that...

@WayneWerner: I'm just going to leave this here. https://youtu.be/ioDGzYsgCfM?t=123

Step 1 not mentioned so far: keep the unconscious pilot from slumping forward into the controls.  Their body pushing the yoke in would be a bad thing at this juncture.  Cinch up on the shoulder harness and hang the flight bag strap or something similar on the pilot's forehead, with the bag hanging behind the seat.
Then do all the other things in the excellent answers here.
Many years ago I had my wife take a one-day course on exactly this scenario, called the Non-Pilot Pinch Hitters course.  I don't know if it's still offered anywhere, but I found that AOPA has a flash version online.  It is most important to familiarize your flying companion ahead of time (assuming it's not a dog) with the radio and how to keep the wings level.
Here is the checklist from the AOPA course:

Even the dog could benefit from familiarising themselves beforehand, if they're this dog.

Here's my guess as a non pilot.
You'd probably have to ask your friend in advance how exactly to do 3. I suspect doing 1 and 3 simultaneous will be taxing for anyone who hasn't flown a real aircraft.
You might want to know how to set the transponder (if present) and what code it should "squawk".
If the pilot passed out immediately after take-off before reaching cruise altitude, you might not want to maintain that flight level - there might be trees or hills ahead.
I think the pilot's order of priorities is aviate, navigate, communicate.

Sounds wise ;) Let see what pilots have to add!

Yes, I read about that aviate, navigate, communicate. But here it will be more like aviate, cry for help, navigate... Since I'm not supposed to know where to go ahah

Navigate does not mean "where am I supposed to go" in this situation.  Aviate - keep the plane flying; navigate - keep it flying where you need it to go - e.g. away from obstacles, towards a clear area etc; communicate - tell someone about it.  Many have died because they did not do it in that order.

Regarding number 3, if you know how to do it in a flight sim, you probably know how to do it in a real airplane. It's not that hard. If the pilot already had the appropriate frequency tuned, it's literally as easy as just pressing the little button on the yoke in most light GA planes. Changing transponder codes is also as easy in real life as it is in a sim. You're right, though, that 1 can be a challenge at first if you've never done it in a real airplane before (assuming no auto-pilot.)

The feel of the controls is one of the things that you will really have to get your head round really quickly if this is the first time you have touched them.
You don't move the controls you just apply a little bit of pressure, unlike a flight sim which has a totally unrealistic feel on the controls, and this alters with the airspeed of the aircraft. You have to be able to handle the aircraft quite precisely to be able to safely land, whereas most people even with flight sim experience take quite a few hours of instruction to be safe enough to go solo.
I read about a crash in the UK where the pilot was incapacitated and the passenger had been shown how to bail out. He couldn't get the hood open because it was heavy and the aircraft hit the ground with him clawing at the hood. All he needed to do was pull the stick back and he would have had more time.
I would say, feeling the controls, just try to get the aircraft level and under control and at a constant speed, will be more difficult than you think it might be, and also to stay calm so you can think and relate to what air traffic are saying. This is a lot easier said than done given that you are just about to die if you do something wrong.
Just a small thing like not already talking to air traffic and not knowing the emergency frequency (or not knowing where the transmit button is) could panic you and ruin your whole day, or pulling the mixture back instead of the throttle. There are loads of things that could go wrong in real life even though you can fly the sim through a keyboard.
On the other hand if you can reach the ground under control at the correct (slowest safe) speed - about 1.2 - 1.3 times the stall speed, you don't need to speak to anyone or do anything else, the chances are you could live, especially if you reach the ground on an airport where there are emergency services to extract you from the aircraft. But then, you might know the stall speed in the sim, how do you really know it in the real aircraft you are in at the time? None of this is as easy as you think!

Just thinking Quentin Hayot. If you really want to know how YOU would react in this situation, why not go to your local airport and book a half hour trial lesson? I am sure that most flying instructors would love to try this with you. Tell them what you would like to do and you want no comments or guidance whatsoever from the instructor at any point, and that you will have the de-brief after the flight rather than before. If you are flying safely, the instructor will let you land the plane. You won't be as scared as if it really happened, but I'd be very interested to hear how you get on :-)

That's a cracking suggestion!  We could have a community whip round for it.  I'd contribute to hear that experience.

I'll contribute too. I landed a full motion 737 simulator recently in a similar scenario and its the best thing I ever did, because there are plenty of more senior pilots saying a private pilot couldn't land an airliner safely. I was so pleased a) I booked it and b) that I lived...

So just to re-iterate my idea - tell your instructor to pretend he is air traffic, call for help, ask him what speed to fly etc etc, and tell him to pretend he is not there so he can't use his eyes only his ears, apart from to save both your lives that is... Exciting!

I had a 747 sim session last year. In a real training simulator. The instructor was in the right seat and was guiding me, but I managed to land it every time :)

@PhilipJohnson I'm not sure that an instructor will accept to do this if I never met him before haha ! But I'll definitely get my licence someday :)

@Quentin Hayout Instructors are all crazy! Of course they'll do it! :-) Seriously doing something different like this would really interest them!

@PhilipJohnson In France they are not that crazy ahaha

@QuentinHayot There is nothing crazy about it.  It could be done in a completely safe manner.  People are given the controls with no previous experience on every first lesson.

When I was... 8 maybe? I was given controls on a Cessna by a private pilot. Reading this thread reminded me of how touchy banking is.

Yes and even assuming you are in trim, if you bank and get adverse yaw and then decide you don't like banking and you are going to use the rudder instead... I can think of lots of things that could go wrong. For example you come into land (under instruction from the tower), put down 2 stages of flap and then decide you need to go around. You increase the power and then really have to push the control column forwards and hold it because the aeroplane is out of trim and its trying to climb too steeply by itself until you re-trim it. If you didn't push hard you could stall and crash...

Having spent a lot of time on flight simulator, and having done an intro lesson, is a big factor in your favor, because you know how to steer, ascend, descend, and especially trim for speed. What you may not know is how to work the radio, how to tune to 121.5 and how to press the talk button (and most importantly, release it). Then the only other thing that might be new to you is landing. So if they guide you to a long, wide strip, aligned with the wind, all you have to do is "ride the slide", and pull the throttle when you get to the ground.

As much as possible, keep your hands off of the controls.  A properly trimmed airplane will maintain straight and level flight.  A human likely will not.
Tune the radio to 121.5 and call mayday.  121.5 will be monitored everywhere there is any ATC activity.
Follow the instructions of ATC.
Use the trim and throttle to descend.  During landing, the elevator (pull back and push forward on the wheel) controls airspeed, the throttle controls altitude.  Trim the airplane and use the throttle to control descent.  More/less trim may be required.

A properly trimmed airplane won't necessarily stay straight. Keeping the wings level with the horizon is a good idea and not all that hard to do, even for the untrained and especially not for someone with a lot of flight sim experience (as the question states.) If you keep the wings level, though, then a properly trimmed plane will indeed maintain roughly the same altitude. If you let the wings start banking, you'll starting descending slowly, too.

Only if the problem happens in straight and level flight!


text:
Why do planes need line of sight for GPS to work?
Why is the below true when mobile devices such as mobile phones and designer watches with emergency beacons work without Line of sight?

Most commercial aircraft transmit their GPS-based position twice per
  second. This is part of their ADS-B broadcasts. The problem with
  providing world-wide receiver coverage for this system is that the
  frequency it uses only travels line via line of sight, so it won't
  travel past the horizon.
Providing coverage over large bodies of water would require a network
  of buoys, which would be quite expensive.
Another possibility is to put ADS-B receivers on satellites. This
  concept is being developed by Thales Alenia Space and Iridium (Aireon)
  at the moment. The first satellites will launch next year, the system
  is expected to be operational in 2018.

From: Why don't all commercial aircraft transmit GPS data in real time?

I'm not sure what your question is (what you've posted seems like it wants to be a comment on something else), but you are incorrect about moble phones working "without line of sight" - they require (radiotransparent) line of sight to the cell tower (to make calls, send/receive data, etc.), and (radiotransparent) line of sight to GPS satellites to fix their position. PLBs (and ELTs) also require line of sight to the satellites monitoring for those signals: Put one under some concrete, or in deep enough water, and it's effectively useless.

Are you asking about how GPS works (your title) or how ADS-B works (question body)?  Both require line-of-sight, but getting that to a GPS sat in a plane is normally easy.  While getting it to an ADS receiver may be more difficult.

mobile phones and designer watches with emergency beacons work without Line of sight who told you this?  Your question is broken since this statement is wrong.

I voted to repoen because the OP seems to be confusing ADS-B and GPS. We should clarify this point in answers to this question, since other people are likely to ask the same question. In fact a couple months ago, someone IRL asked me why GPS didn't work above the oceans for planes after they saw a local news report.

not only is the assumption wrong that line of sight isn't needed, but it's also wrong that there's no line of sight to GPS satellites, AND it's wrong in that GPS receivers don't transmit data.

I understand the question as GPS and ADS-B needs line of sight (as per linked question), this is contradictory with other devices like our mobile phone and wrist Argos / Inmarsat emergency beacon which don't require it. And the answer could be: because the latter two actually benefit from reflection, which allows LoS to be a broken line (but still a LoS), but the signal is weakened with each reflection.

@mins Which would also be true for aicraft systems.  It just so happens that most of the time, they have unitnterrupted line of sight.  Additionally, the reflections are a minor part of the story.  Far more important are the RF lines iof sight and what materials lie in the visible line of sight which cause attenuation. When you're in your house using your mobile, most of the signal is directly received. It may have passed through several buildings and your wall/window. Most things betweee you and the cell tower are lousy reflectors of RF.

@Simon: Yes absorption, reflection, refraction, traversal... is the ordinary life of radio signals. Starting with a reflection for most hi-frequency ones when they are sent backwards and reflected by the parabolic reflector of a dish. That's not different from light paths, which are anyway the same kind of waves.

@mins Except in the case of intentionally reflecting (focusing) off a dish or some such thing, reflections are more often actually actively harmful in RF communication systems. They cause the receiver to receive multiple copies of the same signal, but with a phase shift and different power level. Special designs are used at the physical layer to filter these out. The wonderful world of multipathing.

@reirab if you read what I wrote that's exactly what I wrote. OP is under the impression that GPS receivers transmit data, I told him they don't.

@jwenting Ah, right you are. I missed the 'in' and read it as "it's wrong that GPS receivers don't transmit data."

tl;dr: Mobile devices and designer watches with (RF) emergency beacons don't work without line-of-sight to some kind of receiver. Most types of RF communication signals require a close approximation of line-of-sight between the transmitter and receiver to work.

All GPS receivers require line-of-sight to fix their position. However, this line of sight is up (because the satellites are in orbit,) which is usually not obstructed unless you're inside a building, under water, under a bridge, under ground, etc. Any GPS receiver will stop working under those circumstances. Airplanes are very rarely in situations where their GPS receivers don't have a working signal, except when they're in a hangar. Since they're normally above ground and outside, they normally have no problem getting a GPS signal.
Where the problem comes in is transmitting their location back to someone who's listening for it. This requires either radio communication to some ground-based system (or another aircraft,) such as the ADS-B receivers mentioned in the question. (Roughly) line of sight is required for this. The same is true of mobile devices. They also must be in range (which is often less than line-of-sight) of a receiver that is listening for their location transmission. In the case of cell phones, these receivers will just be cell towers. This is why, for example, we can't just track down the position of some crew or passenger's phone when looking for a boat or aircraft that has gone missing at sea (where there aren't any cell towers in range.)
Note that radio-frequency signals (such as ADS-B or cellular communications) can penetrate some objects, but this ability is very limited, especially as you move to higher frequencies. Thick, dense objects (like concrete parking garages, overpasses, and tunnel roofs) will reduce (attenuate) the signal faster and conductive objects (such as water or metals like copper or aluminum) will nearly eliminate the signal with only rather thin layers. Also, in general, higher-frequency RF signals will be attenuated much more quickly than lower-frequency ones. This is why your home Wi-Fi or a cell phone works through perhaps a few walls, but the new 60 GHz wireless networks wouldn't.
In the case of cell phones, the broadcast range is also intentionally limited so that more towers using the same channel can be packed into a smaller area to serve more people. If they didn't do this, there wouldn't be enough bandwidth to handle all of the cellular communication needs in densely-populated areas.
The Earth's surface happens to be composed primary of rather dense soil and water, so radio signals don't travel through the Earth much at all. In general, any form of radio communication must either have no land or water between the transmitting and receiving antennas or else cause the signal to reflect off of higher layers of the atmosphere or curve around the Earth. Neither of those things works well in the frequency bands used by cell phones. It does work at some of the lower frequencies used by amateur radio operators and such, though.
Communications systems that need to work far away from land or otherwise in remote places where receivers can't reasonably be located within line-of-sight range on the surface will normally use satellites. This is because Earth is not between you and a satellite that is above you and, thus, isn't blocking your signal. Even connections to satellites don't normally work when the satellite is below the horizon (again, due to the Earth attenuating the signal,) but satellite communication systems are normally set up in constellations that are designed to keep at least a certain number of satellites above the horizon in coverage areas at all times or else are set up in geostationary orbit where they will always remain directly above the same surface position.

What if they get the ADS transcievers to themselves act as routers for traffic? The packet size shouldn't be too large since I doubt these messages are bandwidth hungry. At any given time the likelihood that another plane is in line of sight must be quite good? At least better than having a ground station in line of sight.

@curious_cat Aside from needing to redesign ADS, the biggest problem I see with that immediately is that it would be chaos in busy airspace. You couldn't just blast back out every ADS-B broadcast you received because then you'd have infinite retransmissions. You'd pretty much have to set up a mesh network, but that would become intractable quickly with the physical locations of the nodes moving relative to each other at well over Mach 1. You'd probably jam the channel just with routing configuration messages.

@curious_cat It might work a little better if you only enabled it, say, on trans-oceanic (or otherwise very remote) flights.

Exactly. The protocol could distinguish between land based receivers and airborne routers. If a land based receiver is contactable then a handshake happens and things proceed the usual way. If no land based receiver is found then a different kind of packet is sent to which airborne receivers respond. I'm sure the protocol can be made robust enough to avoid infinite re-transmissions etc. with a TTL field, tweaked routing protocols  etc.

The airborne routing transcievers with the most viable  / robust path to a land based station could respond and then a fixed route is followed until that path starts fading and then a new route discovery packet is sent. Mach 1 sounds fast but that's relative to sound. Relative to EM transmission I'm sure Mach 1 is insignificantly slow. The tricky issue might be how soon line of sight gets lost at Mach 1. i.e. How unstable would be the discovered routes and how often would route discovery packets (i.e. overhead) need to be sent.

@curious_cat Mach 1 is a little over 0.0001% of the speed of light, so propagation delay between nodes should not be of any concern. Other problems would overshadow this, some of which have been mentioned in this comment thread.

@curious_cat The tricky issue might be how soon line of sight gets lost at Mach 1. Yes, that's why I mentioned it, not for propagation delay. That and, even moreso, how quickly nearest neighbor/best path through mesh change in such an environment, especially near a busy airport.

@reirab: You couldn't just blast back out every ADS-B broadcast you received because then you'd have infinite retransmissions Yes, adaptative networks are able to manage this. This is likely the future of networking, like between cars.

@mins Right, but the ones between cars are intended for low-power transmissions to nearby cars, not to airplanes hundreds of miles away. The lower power levels involved allow for much better channel usage (because each transmitter isn't blocking the channel over a ~60,000 mi^2 area.) Additionally, the more uniform velocities involved don't require quite as much reconfiguration of the mesh as when the nodes are moving around more or less freely in 3 dimensions at high speeds. Also, the propagation delay is much less with the cars, which makes bidirectional protocols much more useful.

This talk of mesh networks is massively over-complicating things. The 'correct' solution would be to use a satellite uplink to transmit the ADS information.... We already do this to some extent (see MH370's handshake used to track the aircraft), and could easily use it for more

@JonStory Agreed. Though, it was ACARS that was used to track MH370 rather than ADS, IIRC. An update to ACARS using something other than 1970s technology would probably be the best solution.

You are asking about two very different, unrelated technologies.
GPS is the technology that determines the receiver's position based on signals from satellites.  Those satellites are overhead, so line-of-sight is pretty easy. (airplanes usually don't fly in caves, buildings or other places where the overhead view is blocked)
ADS-B is the technology that broadcasts the position determined by GPS to other airplanes and ground receivers at regular intervals.  It also requires line-of-site between the sender and receiver. (more-or-less: slightly indirect routes will work if the signal is not degraded too much)
You also claim that cell phones and other devices don't require line-of-sight.  That is only true to the extent that the direct line-of-sight isn't terribly obstructed, which is usually related to how nearby and how powerful the transmitter is.  You don't always get cell phone signals in the interior of large concrete and metal buildings, or deep in parking garages.  It is also why cell-towers are mounted up high and in locations where they can see a lot of terrain.

GPS satellites transmit a very weak signal. About 60 Watts are irradiated at the satellite, arriving at earth's surface with just miliwatts of power.
so anything in the line of sight between the receiver and the satellite will block the signal.
A mere mili meter tin foil will do it.
This is mostly a problem in the ground when surrounded with skyscrapers or tall mountains, because there are usually 31 operational GPS satellites in the world, with a full view of the sky we typically receive 11-13 satellites. So even with the first 5 degrees from the horizon blocked we should still typically get something like at least 7 satellites, when just 4 are essential and 5-6 help improve the quality of the fix substantially.
But if the bottom 30 degrees (or more) from the horizon are covered in every direction we start running into the possibility of not having enough satellites to properly calculate a 3D fix (4 satellites). This doesn't happen all the time.
For aviation GPS this isn't a problem for en route, cruise climb/descent situations. But during taxing, initial climb and critically instrument approaches there are airports where GPS can't be relied upon.
In the future we'll use a mix of USA GPS, Europe Galileo, Russian Glonass and other GNSS constellations, ensuring proper reliable coverage 24x7 even in airports surrounded by mountains. With 4x as many ranging sources, there are always enough satellites above a 45 degree angle that you'll always get a good fix.

a few sources would be nice.

The information presented is the result of day by day usage of GPS receivers, some engineering knowledge and a few things I read here and there. I don't have sources, because they are my own conclusion. Many numbers are estimates.


text:
Is it possible to perform the Lomcovak manoeuvre in a C152 aerobat?
Has anyone performed a Lomcovak manoeuvre in a C152 aerobat, is it even possible, or would that likely overstress the engine?

@jjack: the 152 Aerobat is sturdier than your typical Cessna, rated +6g / -3g. Doesn't mean it could do a Lomcovak, but it might be strong enough. Depends a lot on the engine & engine mount, I imagine.

Yeah, but the Lomcovak is primarily negative g, right? Is the Zlin that did the maneuver +/-10g?

The list of approved maneuvers is in the POH, and I'm sure the Lomcovak is not listed. If you are willing to do unapproved maneuvers, the issue is that because the aircraft tumbles rather than flies in this maneuver you have a few things to worry about: it starts with an outside maneuver, it is inverted, and the exit requires a high-speed dive which will exceed Vne or the +6g the 152 Aerobat is rated for.


text:
What are these "patches" on an Airbus A321 wing?
While on a WizzAir flight I noticed on the wing the patching marked in this image:

I'm just curious, not implying lack of safety or whatever else. Why the wing is patched that way? I mean why the two small patches, the apparently missing a bit of the cover, and...why the leftmost patch is between other parts?

Looks like a crack repair to me, or patching for some other kind of damage.

Repairs on the left engine pylon visible on this video from HA-LXA. Also this one.

Yikes! That aircraft was less than a year old when this question was asked.

@mins: in all honesty...I never asked what specifically happened to that exact plane (otherwise I'd have written it that way). I'm asking about general knowledge, reasons for patching a plane like that, if it's a typical work done on planes, etc. etc. No need to know if the plane had some specific problem in the past or what, just seeking knowledge.

@FreeMan: It was even repaired in the 2 weeks following its delivery on 12 Nov. 2015, since the video above was posted on 27 Nov. :-( I've also this view with the reverser open.

It's possible that the repair was done when the aircraft was new. If an area is known to be subject to crack propagation, then perhaps strengthening plates are fitted at build time as a cheaper alternative to redesign and retooling?  Just a guess.

Looks like they are there from manufacture

I am not familiar with that particular aircraft but I would hazard to guess it is not a patch.  I say this as I have never... in 20 years of aircraft maintenance... seen a patch that incorporated screws.  If this were a patch for a crack in the sheet metal it would be rivets all the way around.
AC 43-13 standard practices is the general reference for skin structural repair although manufacturers will publish their own Structural Repair Manual with their own preferred methods.  And certainly I have seen design Engineers come up with odd things to deal with AD's etc.  But I have never seen screws used as a method for installing a patch.
So... I would say it is likely a designed in strengthening piece. It is also a single piece if you look at it carefully it contains a Joggle which makes it look like two separate pieces.  A Joggle being a step in the metal to account for two different surface heights.

Correction... AC43-13   My fingers went back in time to my Navy days...

You can edit your post directly for corrections, rather than using a comment. I've edited for you.

@HowieMurray This answer quite a bit, but not entirely. A "words of god" would be much appreciated, if you work in maintenance, maybe you could ask around? A thing that struck me even more than the screws are the total lack of a cover. As it seems from comments to my question that this could come right from production, and with all the cares companies take to develop a plane, I find really odd that there is no covering for that part and it's instead let in open vire.

authors: Деян Метанов


text:
How many angle-of-attack sensors does the Airbus A 320 NEO have?
Are there 3 x AOA-sensors on all the Airbus family planes? In the Airbus flight manual there is one AOA-sensor called 'stand-by'. What does that mean?
Are all 3 AOA-sensors heated and can the actuall temperature of these sensors be monitored live by the pilots during flight?

I think there are three angle of attack sensors in all Airbus planes using fly-by-wire systems. The first two, which are arranged symmetrically near the nose are the main ones and the third one in the aft.
The angle of attack data is not typically displayed to the pilot. The computer, on the other hand displays only stall warning.
The angle of attack sensors are heated and active at  all times. The data from the sensors is received by the computer, compared (voted on) and displayed in the cabin.  The computer needs two values to agree for display.In case one fails or no two agree, the stall warning is lost.
The main use of the angle of attack sensors is their use by the computers in calculating the characteristic speeds and for providing stall warning. I don't think the pilots can monitor. let alone control the heating of the AoA sensors.

Is there an additional analog or whatever AOA-sensor if all 3 sensor should fail at once?

No. It doesn't make sense to put a whole lot of sensors in the aircraft and there are only a few places you can put the where they are effective and not too near to each other.

Does a deployed Ram air turbine deliver any angle-of-attack data by itself or would it deliver enough power to run all the sensors in case of an electrical failure? Very special question, I know.

@ErasmusVertigo It certainly can run the sensors in case of electrical issues

'#1 sensor data is displayed on the pilot's display by default, #2 sensor data is displayed on the co-captain's display by default, #3 sensor (stnd by) data is not displayed but is waiting for one of the other two to fail and it will display in the failed ones place.
They are all heated and active at all times and the pilot's can choose which ones to use on any display or flight control interface.

I guess there is no temperature feedback display if rare condition occurs one or another AOA-sensor freezes? THX.

Do you have any reference where it is displayed? Because according to what I've seen AoA is not displayed anywhere, but that was for CEO, so maybe they changed it in NEO.

That is a very generic answer, and also factually wrong, as all three AOA values are compared to each other to detect possible errors. You cannot switch the AOA sources themselves around. You could, however, switch the ADR 3 assignment to CPT or FO side in case of a failure.


text:
Does Airbus provide pitch control correction symbols outside "normal law"?
Do pitch control correction symbols exist in 'alternate law' and in 'direct law' mode (if planes angle of attack exceeds dangerously)?

IIRC they are drawn in amber indicating that the corresponding protection is not available (in alternate law only some protections become unavailable, depending on the reason to enter alternate law), but I would have to look it up to be sure.

By "pitch control correction symbols" are you talking about the flight director indicators?

You may be confusing the operation of the autopilot, the envelope protections and the flight director.
AIUI, the job of the flight director is to indicate the required roll angle and pitch to achieve a new compass heading and/or new altitude that the pilot has selected on the FD. If the AP is engaged, the FD will cause the AP to make the appropriate control movements, otherwise the pilot has to make the control inputs suggested on the FD display.
This has nothing to do with flight envelope protections AFAIK.
In Alternate Law the Flight Director can still be visible.
The BEA identified misuse of the FD as a possible factor in the loss of AF447

as the flight control law switched from normal to alternate, the flight director’s crossbars disappeared. But they then reappeared several times. ... PF may have trusted the flight director so much that he was verbally agreeing to the other pilot’s pitch-down instructions, while still actually pitching up.

AIN online

Disconnection of the flight director is normally part of the "unreliable airspeed" procedure. But after the A330 lost its airspeed information, and the autopilot and autothrust automatically disconnected, the crew left the flight directors engaged.

FlightGlobal


text:
Why are passenger required to put their phones in Airplane Mode during taxi to gate?
Why do airlines require that phones remain in airplane mode during the final taxi to the gate after landing? As far as I can tell, it does not affect the airplane or anything else negatively or at all. Is this true? If so, then what is the point in keeping the phone in airplane mode until the cabin doors open? Is it just for the sake of convention?
Thanks a lot in advance for any responses!

Not all airlines require this. For example, Air New Zealand lets you turn on your phone as soon as the aircraft leaves the main runway. So, it's a matter of policy specific to your airline.

In general, they don't. U.S. airlines generally allow you to use your phones as soon as the plane lands.
Southwest:

Effective today, Southwest Customers with cell phones onboard may begin using them after the flight attendant gives permission to do so upon landing at the destination and taxi to the airport gate.

Source: Southwest Press Release from Sept 2, 2003
Delta:

Use of cellular devices prior to takeoff is not allowed per Delta policy so that flight attendants may properly prepare the cabin for departure and conduct safety demonstrations uninterrupted. Cellular devices may be used upon landing as instructed by the cabin crew.

Source: Everything You Need to Know About Using Devices on U.S. Airlines

Perhaps of interest, the rule against using cell phone during flight in the U.S. is not an FAA Federal Aviation Regulation. It is instead an FCC (Federal Communications Commission) regulation designed to prevent interference to the cell network as a result of thousands of phones flying around at 600 mph hitting hundreds of cell stations at once. In general, the FCC acknowledges that this rule is outdated and that this is no longer an issue for the current cell network. As such, the FCC has issued a proposal to remove this regulation. However, some airlines (including Delta and Southwest) have publicly stated that they will continue to not allow cell phone use for voice calls during flight even if it is legal, as the majority of their customers have indicated that they don't want to listen to their neighbors chatting on a cell phone for hours on end.

Delta will not allow cellular calls or internet-based voice communications onboard Delta or Delta Connection flights. Our customer research and direct feedback tell us that our frequent flyers believe voice calls in the cabin would be a disruption to the travel experience.
In fact, a clear majority of customers who responded to a 2012 survey said they felt the ability to make voice calls onboard would detract from – not enhance – their experience. Delta employees, particularly our in-flight crews, have told us definitively that they are not in favor of voice calls onboard.
-Delta CEO Richard Anderson

It is so nice to hear that so many people will speak up for common courtesy, even though so few actually practice it. /rant

Is there a reason for why the phone has to remain off until finished taxiing to the gate?

@Dopapp At least on the above listed airlines, it doesn't. The wording is a little awkward in the Southwest quote, but they mean that it's allowed after landing during the taxi to the gate. They'll usually make the announcement that cellular devices may now be used as part of their "On behalf of Southwest, welcome to ..." announcement, usually right around the time the aircraft begins exiting the runway.

I just landed yesterday (noonish) and they told us to open the window shade things. I was flying delta

@Dopapp Did they actually tell you not to use your phone while taxiing to the gate? I've never had anyone on Delta say that before (and I usually fly Delta several times a year.) Sometimes they don't make the announcement that they're allowed right away, but I usually turn mine back on (and often call whomever I'm meeting at the airport) right after we leave the runway and I've never had any FA complain about it.

@reirab - huh. Maybe it's just an anomaly of sorts.

Regarding the FCC rule: it applies only to certain frequency bands. I don't think any current-manufacture phones even use those bands any more.

@ammPilot That does not appear to be correct. The 47 CFR 22.925 says, "Cellular telephones installed in or carried aboard airplanes, balloons or any other type of aircraft must not be operated while such aircraft are airborne (not touching the ground)." If you can find an authoritative source, though, then I'll edit the answer.

Thanks for the comment, @reirab. Digging further into current info, 47 CFR 22.905 specifies the channels for the cellular service governed by 47 CFR 22 to be 869-880 MHz paired with 824-835 MHz, 890-891.5/845-846.5 MHz, 880-890/835-845 MHz, and 891.5-894/846.5-849 MHz. AT&T, for example, mostly uses other bands (700, 1700/2100, and 1900 MHz), but can also use 850 MHz (both on 4G and on LTE). So, I rescind my comment, with thanks, based on the technical details (unless you can control which band your phone uses!).

Though all systems are gone through series of electro magnetic Tests in the Lab. The mobile phone signal may contribute enough electro magnetic interference in the real world. Due to this electro magnetic interference the systems may start behaving differently and erroneously. Take off and Landing are the crucial stages of flight phases, it is always better to avoid the chances of taking risks. If 1 mobile phone can produce this, you could just imagine about the all passengers turning on their mobile phones and contribute the interference.

Note that cell phone use is not forbidden by FAA (in the US), but by FCC. In Europe EASA allows cell phone use. This has more to do with telco, than flight safety, but is presented to public as a safety measure. See this. An equipement that would be sensitive to 2W at 1 or 2 GHz would likely not be certified for an aircraft. The overall ban on cell phone use in flight makes sense as a regular ground cell network is not designed to connect high speed "clients".

Note that no U.S. agency prohibits use of cell phones in a taxiing aircraft. FCC only bans it while airborne and is studying the removal of that rule.

Your answer talks about the potential danger of using a cell phone while the plane is landing. This is irrelevant to the question, which is about using cell phones while the plane is taxiing to the gate after landing.


text:
Why isn't the airspeed indicator the primary instrument for power during a constant speed climb?
I am studying the primary and secondary IFR instrument designations. I understand that the primary instrument is the one that closest represents your target value, and is normally the one gauge that isn't moving on the panel during the targeted maneuver (for example, in a constant rate turn, the Turn Coordinator is stabilized on a value after entry is completed and becomes primary).
I fly a variable pitch prop, and I think my confusion might be a result of not flying a constant speed propeller.
Take a look at the item in red:

Question:

Can someone explain why the CS Climb power primary isn't the airspeed indicator?

If you are stabilized on your airspeed, wouldn't airspeed dictate the power setting you want to maintain? If you change pitch, the airspeed drops/rises and the power is changed - doesn't that make the airspeed indicator primary?  I have been taught to set power (on entry) and then monitor airspeed to make pitch adjustments. This makes the idea of a power primary confusing in stabilized descent/climb.
This seems like a confusing way to have to learn the material as I don't find I have to think about this while flying to effectively control the airplane...

Airspeed indicator is a primary instrument for pitch in that row, so it can't be also primary for power.
The point of constant speed climb is that you select power and maintain speed with pitch, getting whatever climb rate that power can support. Most often the point is selecting "climb" or "maximum continuous" power and climbing as fast as possible without overstressing the engine.
The only difference with variable pitch prop is that it decouples rpm from engine power, so you can't use rpm and are left with manifold pressure only (for piston; I am not sure what the correct reference is for turbine).
Note that two lines lower there is a constant rate climb and there airspeed is primary reference for power, because there you adjust pitch to maintain desired vertical speed and power to maintain airspeed. But since you shouldn't use more power than the recommended climb setting anyway, the constant speed climb gives you better performance.

Makes a lot more sense than what I was coming up with - talking myself in circles. Thanks!

@Charlie, the term constant speed climb might be somewhat misleading, because the constant rate climb is also flown with constant speed.


text:
Is it safe to roll an airplane that isn't approved for it?
I have heard of pilots rolling airplanes that aren't approved for it (Cessna 172, Learjets, etc.), and other than the obvious legal issues, are there any mechanical or safety reasons to avoid it?
DISCLAIMER
I do not advocate doing anything (like this) that is not legal, but am looking more for additional reasons that I can use to dissuade people from doing this when they say that it isn't hurting anyone or something along those lines.

Wouldn't it be approved, if it were safe to do so?

@kjmccarx Not necessarily, the aircraft manufacturer may not have wanted to spend the money to certify that with the FAA due to the cost.

@SpongeBob: Also remember that while barrel roll does not involve any unusual loads and should be doable with almost any aircraft, an average pilot not trained for it may easily loose spatial orientation. A business jet crashed couple of years ago because the pilots (it was ferry flight, so only the pilots were on board) wanted to try a barrel roll and lost spatial orientation.

There are a lot of good reasons not to roll such an airplane.

If the plane has gyroscopic instruments, you might tumble them (cause the spinning gyro to hit the inside of the instrument).  This can be expensive.

You might easily over-stress the air frame.  Normal category light aircraft are rated to -1.5 to +3.8Gs.  (That's for a new aircraft)  A botched roll can easily hit 4.5 or higher.

If you over stress the air frame, you might just put a lot of very expensive "wrinkles" in the skin that would be very hard to explain to the FBO, your boss, or the insurance company.  Trashing the gyros would be cheaper.
If you're not lucky, the wings fold up and you fall out of the sky.  It's a stupid way to die.

Non-aerobatic aircraft typically have limited elevator authority; once upside down, you might find it very difficult to keep the nose pushed up high enough to keep the roll going.  Turning a botched roll into a "split-S" is one of the worst "recovery" mistakes you can make, and you're setting yourself up for it.

Non-aerobatic aircraft often have gravity-feed fuel systems.  A little bit of 0 or negative "G" and it will get very very quiet in the plane.  Some people consider this silence detrimental to the continued safety of the flight.

Non-aerobatic aircraft rarely have inverted oil systems.  As the engine gets quiet, it also loses most of its lubrication.  Bare metal on metal friction can be detrimental to achieving TBO.

Having said all that, in the hands of an expert, it is technically possible to barrel roll most aircraft.
A good way to tell if you're an expert is to call your insurance company and tell them exactly what you plan to do.  If they'll quote you affordable coverage, you might be an expert.
Obligatory links because if I don't include them someone else will:

Tex Johnson rolling a 707.  I'm pretty sure he'd never get away with this today.
Bob Hoover pouring iced tea.  Bob Hoover is beyond expert.  Way, way, beyond expert.

If you want to roll an airplane, contact your local aerobatic club.  In the US and some countries, it's the [International Aerobatic Club][5].  Get some competent dual instruction in a suitably rated airplane.

I think it was a 707 that Tex Johnson rolled. It was done during a presentation of the plane, in front of the president of Boeing and an FAA representative. There were reporters on board, and one of them managed to get a photo out of the window when the plane was inverted.

And as shown in the Bob Hoover video, a properly-executed barrel roll is a gentle positive-g maneuver all the way through. In theory, you could do this with any plane, as Tex Johnson demonstrated. In practice, don't do this unless you're Bob Hoover.

@EdwardFalk - you are correct, it was a 707.  I've updated the answer.  Thanks

+1 for "Some people consider this silence detrimental to the continued safety of the flight".  That made my day.

Tex Johnson got chewed out by the head of Boeing for that one.

LOL super answer, dude  :)

on thing, the "iced tea" video is actually behind a BBC regionwall in most regions, perhaps someone has a better link for that.

@ColinCochrane Mine too!!

I’d give another +1 if I could for one of the the best universal life hacks ever seen on aviation SE so far: “A good way to tell if you're an expert is to call your insurance company and tell them exactly what you plan to do. If they'll quote you affordable coverage, you might be an expert.”

Tex Johnson's roll was the result of an expert test pilot, keeping the aircraft at 1G during the entire roll, so the aircraft wasn't stressed and the lube systems weren't affected. Most weekend pilots don't have the experience to pull that off and keep the G forces constant throughout the roll. An impressive display of precision piloting.

Points #3-#5 seem to be referencing the type of roll ("aileron roll"?) where the G-loading goes negative when the aircraft is inverted.  The definition of "barrel roll" may not be entirely universally agreed on, but it's not that.  (Definition of "aileron roll" may not be entirely universally agreed on either--I've seen some rolls that stayed positively loaded described as "aileron rolls", they just involve less total heading change than a "barrel roll".)  A "slow roll",  on the other hand, unambiguously goes negative.  Maybe there's a new ASE question in the making here.

A barrel roll, when properly executed, does not put the aircraft through any unusual stress and is possible with almost any aircraft.
However it is only true if it is properly executed. Make a small mistake and you can easily put more stress on the aircraft than it can handle, put it to a spin, starve the engines of fuel (if you let it slip into negative G) or simply loose spatial orientation (especially in older aircraft with mechanical gyroscope that would tumble) and then you'll end up like these two pilots in Cessna 550B Citation in Germany in 2010.

A barrel roll is not a ‘cross-controlled’ manoeuvre. Done properly, the slip/skid ball stays centred, a glass of water on top of the panel will stay in place with the water level exactly even. You could leave your seat belt unfastened and Mr Hoover could pour you a cup of tea.

Do not even think about it unless you are an expert. I read about an incident in Sport Aviation in which a non-aerobatic performer rolled a piston twin. The airframe was overstressed and it broke up in flight. All four on board were killed.

What if they are an expert aerobatic performer?

authors: นิติพล บินโส๊ะ


text:
Is spin recovery possible in an airliner?
During initial flight training a lot of emphasis is placed on stalls and spins and how to recover from them, but is it possible to recover from a fully developed spin in an airliner? Do these large aircraft have enough rudder authority to pull it off?
Has it ever been done? And is it part of the training for specific type ratings? (in a simulator of course)

Actually, most of the initial flight training regarding spins is on recognition and avoidance, not recovery.  Good question though!

Of course, but you're also expected to know how to recover from a fully developed spin. Although rather uncommon these days, some instructors still want you to demonstrate it during training (in a spin-approved aircraft of course).

Here in the US, actual spin training is only required for your flight instructor certificate.  This may be different other places though.  In any case, I was just nitpicking the first sentence.  I'm curious about the answer myself!

One of the reasons why I'm asking is because of a few famous stall/spin accidents involving airliners (Colgan Air 3407 for example)

Colgan Air 3407 was a case of a captain getting himself into incipient stall and then providing control inputs to put the plane into a full stall.  That case has no bearing on the ability to recover from a wing stall, as the crew never attempted to do that.

@casey Did you read the question? I asked if it is possible to recover from a fully developed spin, not a stall. I was just referring to Colgan 3407 to illustrate that airliners do stall, despite stick shakers and pushers. So it is not inconceivable that an airliner can enter a spin and I am simply asking if it is physically possible to recover if the airplane is already in a spin. How it got into the spin is not part of my question.

Interesting reads: http://www.pprune.org/flight-testing/226351-spinning-airliner.html and http://www.airlinepilotforums.com/hangar-talk/6370-spinning-airliner.html

I would say it depends of the airliner, but China Airline 006 tends to prove it is possible (even though I don't know if this could be qualified as a fully developed spin), at least for the B747SP.

The problem with your question, which is an intriguing one, is that you'd need to ask this question for each model of aircraft.  Depending upon design (such as the high tail of some previous airliner designs) even the stall characteristics (and chances for recovery) will vary from model to model. (Deep stall was potentially unrecoverable, for example).  The other issue to consider is what control inputs are specifically "pro spin" control inputs for a given model.

There were a lot of other mitigating factors in the Colgan Air 3407 crash. Was that one recoverable? It depends. It never should have got to the point of a stall in the first place. It was more preventable than recoverable.
But in answer to your question, again, it depends. Every aircraft in the air can stall and be recovered, if responded to properly. But the plane may very well bend and break if the stall develops too far. Then it may not be recoverable. And most large airliners (or aircraft bigger than a few thousand pounds with multiple engines) aren't designed for the stresses of spins, so they never teach to a full stall. In those types of aircraft a full stall is much more dangerous, and they can be much more difficult to recover from, especially if you break something. Besides, in aircraft like that, you should receive plenty of direct warning long before you reach the point of a stall.
When I was teaching, stalls and spins were one of my favorite subjects for early pilots. Especially in light trainers like the Cessna 150/152s. Those aircraft were always incredibly good at stalls/spins and incredibly forgiving. You can put a Cessna into a hands-off full stall if you trim it right, and it will stop rotating in a spin if you simply let go of it (and have enough altitude). I always taught my students spin recovery from a full spin, even at the Private Pilot level. And usually shortly after teaching them full stalls. I would stall it, make it rotate at least 3 or 4 times, and have them recover the spin. Then have them do it themselves. I never had to worry about my students not knowing how to recover from an unintentional stall/spin. By the time my students were learning to fly multis, I was teaching them more stall recognition and avoidance than recovery. Recovery is essentially the same in all aircraft. You just have to be sure to not reach that point.
There's only one thing you really need with any aircraft in a stall/spin, and that's altitude. Unfortunately, takeoffs and landings are the most likely places for you to get behind the aircraft and let it unintentionally stall/spin. That's why you learn how to recognize them very early in your pilot training. You can't spin without a stall first, and just about any airplane will give you fair warning before you stall it. The trick is recognizing the situation before it becomes serious.

Unfotunately, Air France showed that they can still be stalled.....

Also (just my personal opinion here) I disagree with spin training in a Cessna just because it is so forgiving.  People don't respect it the way that they should, because it is just so hard to spin that there is no way it could accidently happen, and even if it did you just have to let go....

@Lnafziger - It all depends on how you teach it. I always taught it more from the angle of "respect how easy it is to unintentionally spin" rather than "see how hard it is to spin this airplane". I liked spinning in the Cessna BECAUSE it allowed me to easily enter a full spin and hand the plane over to the student with the additional margin of error so that they couldn't do something to exceed MY ability to recover.
That's the exact same reason I always hated stall training in a Piper Tomahawk. That plane was VERY easy to unintentionally spin. And it spun somewhat flat. That sucked.

Have you tried to spin at high altitudes like service ceiling? Is recovery more difficult there?

@Andrius No, I have not tried it. But I imagine recovery would be more difficult since the aerodynamics at higher altitudes are different, and controls will be less effective.

@Lnafziger - I gave you +1 but differ slightly in some points. Cessna are not "easy" aircraft to spin train in (FYI also Piper tends to stall much softer then Cessna) All FAA (after CAR 3 - 1959) GA normal category aircraft  are required to recover from a spin hands off within 1-1/2 turns. All small training aircraft exhibit this behavior. With the exception of older mostly rag and tube aircraft, Cessna aircraft have a more violent (wing drop) habit. When I had 10hrs and was getting my PPL in 1975 I switched from Piper to Cessna aircraft specifically because Cessna's are less forgiving.

@jwzumwalt Which Piper aircraft were you flying? In my experience, Cessnas were not "easy" to enter a spin, which is part of why I liked teaching in them. The Piper Tomahawk was the only aircraft I ever flew that unintentionally tried to spin in almost every stall. And when it did spin, it was very flat. That's not very fun. I definitely wouldn't classify any Cessna I ever flew as "less forgiving" than any Piper.

In the sixties a Sabena Caravelle VIN entered a flat spin during a  training flight.
The crew demonstated stall recovery in different configurations when the plane entered into a spin by accident.
The instructor saved the aicraft by pulling the brakechute after
configuration changes showed no result  (the Caravelle VIN had no reverses on the RR Avons but was equiped with a brake parachute in the tailcone). The yaw decreased and the tail was pulled up enough to unstall the wing.The wing had only TE-flaps and no LE-slats.

Yes they will spin.
They appear to have enough rudder authority - big twins have a lot, for engine-out reasons, but I don't know the aerodynamics well enough to state that it's certain to be enough, good question.
No, they have not been spun during test or for training. No, type-ratings don't include spin recovery, just stall recovery in simulators (including FBW types which have to be degraded first to allow them to stall) and recently recovery from unusual attitudes.
Simulators can't generally be used to train anything involving sustained yaw because the physical limitations make it impossible to accurately reproduce the feel. They are not built or approved to model accurately anything outside the approval requirement, which doesn't include spins, so while my large aircraft type's sim spins quite nicely ( I do it quite often, for fun, 'after hours' there's no guarantee, proof or reason to expect that the real aircraft would spin in the same way or be as recoverable.

Most sims use predictive numerical integration algorithms which are only effective in linear phases of flight. In non linear phases (post stall), these algorithms break down very quickly. Not to mention, there often is no post stall data from flight testing for obvious reasons. The net experience in the sim is just an educated guess. In the case of AF447, the yaw damper function did a very effective job of minimizing sideslip and preventing the aircraft from entering a fully developed spin.

Swept wing aircraft are equipped with yaw dampers to keep the aircraft in coordinated flight since swept wing aircraft are more susceptible to Dutch Roll (you can look up that term).
An American Airlines A300 lost its entire tail and spun out of control departing New York in 2001 as a result of a pilot using too much rudder pressure to (over) respond to what he thought was a wake turbulence encounter.
I'm no engineer, but if an airliner can exceed it maximum design limit on the vertical tail and lose the tail as a result of using too much rudder pressure, logic tells me that the vertical tails are absolutely not designed to take the stress of any kind of excessive rudder input (like you'd use for spin recovery), and in fact, the tail just rips off when you get sideways.
(Note that Airbus aircraft have composite tails and there is a known issue with the A300 model having overly sensitive rudder pedals- and the pilot used A TON of pressure on the rudder pedal).
Swept wing aircraft are susceptible to dutch roll.
Recovering from a spin in a swept wing aircraft?
Well, it's kind of like a low altitude spin in a small airplane... if you didn't do your job as a pilot to prevent the approach to stall and ensuing stall... you missed your chance and you're done.

Big airplanes of the jet types have what is called stick shakers to warn pilots of an approaching stall and a stick pusher to initiate a recovery. In training with jets most pilots do 100% of there training in simulators and then make three takeoff's and landings in the airplane.
T tail airplanes may not be able to recover from stalls if the airplane get into a deep stall because airflow over the tail is blocked by the airplane and the elevator becomes ineffective.

My question was specifically about spin recovery, not stall recovery/prevention.

How do you get into a spin.

The Colgan flight entered a spin after stalling. My question was if recovery is possible if you do get in a spin.

@Phil Fountain Maybe post that as a question to get a full answer. Short answer for a light aircraft: put it up into a power off stall, then at the moment of the stall jam the rudder in the direction you want to spin.

@Terry I think it was a rhetorical question. :)

With big aircraft the systems I discussed are used to prevent both situations from happening. The are both interrelated.

@Philippe - Again, it all depends. Under perfect conditions, you SHOULD be able to recover. But if you've already reached a point where you're spinning a large airliner, you're already so far behind the game that you probably won't be able to catch up fast enough to recover. That's why the training tends to focus more on avoidance than on recovery. There's more than enough warning on any aircraft that you shouldn't spin it in normal operations. And if you're flying right, you really shouldn't even come close to a stall.

@Shawn And still they sometimes do manage to stall and spin a big airliner. Hence my question :-)

@PhilFountain As I mentioned in a comment above, even with all of those systems in big aircraft, Air France still managed to stall one...  :(  It can happen.

@Philippe - I would stand by my statement. Airplanes don't just stall under normal operations. So they can't spin either. And if you ever find yourself in a situation where you're stalling/spinning a large airliner, while it should be possible to recover, if you're that far out of the envelope that you allowed it in the first place, you may not be able to catch up fast enough to recover.